For example, in a technological field of a machine tool, there has been provided a machine tool commonly provided with a three-axis driving mechanism for moving a spindle portion for mounting a tool in X-axis, Y-axis and Z-axis directions and a rotary driving mechanism for rotating a support member, such as table, for supporting a workpiece to be worked around a C-axis and/or A-axis (for example, please refer to the following Patent Document 1). In such machine tool, the three-axis drive mechanism is driven by each of liner motors, and the rotary driving mechanism is driven by a hollow motor. More especially, the rotary driving mechanism more quickly starts to be driven by the direct driving of the hollow motor, and a transmission member such as pulley and/or a reduction mechanism may be eliminated in a mechanism for rotating and driving the C-axis and A-axis, thus being effective.
However, in the machine tool provided with both the three-axis drive mechanism and the rotary driving mechanism mentioned above includes many troublesome matters for a practical use or realization, and hence, such machine tool has not been realized in practical use
For example, explanation may be made with respect to a C-axis table as a rotary driving mechanism around the C-axis. As commercial needs of the C-axis table, it is required to provide functions of high performance and high speed rotation for realizing working operation with high performance and high efficiency, and in addition, in relation to light cutting working by a machining center, it is at the same tome required to provide high load bearing performance which opposes to the functions of high performance and high speed rotation mentioned above. However, in a conventional technology, from the requirement of properly rotating a holding member such as table for holding the workpiece around the C-axis, it has been attempted to set such holding member using a general rotary bearing.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-130468.